Ok here are the results of the "free plantation" simulation.
Important information about the results:
1. The woodcutters have no obstruction to plantation of trees. They have absolutely free area for planting trees.
2. I used two styles of placement for woodcutters. "Line style" and "Pair Style". In Line Style all the woodcutters are placed in one horizontal line with one road. In Pair Style the woodcutters are placed in two parallel lines with two roads as shown in the picture below. The "spacing" in this case refers to the inter-pair spacing i.e. spacing from 1 pair to the next pair in horizontal direction. In vertical direction they are always 1 tile distant i.e. only the road.
3. There is some statistical variation in the results. In every simulation I had one standard sample where I have only 1 woodcutter. Even he produced different results in every repetition: varying from 87-91. I think this statistical variation will get broader as the number of woodcutters is increased. So for getting a very reliable result, one must repeat the simulation many times (e.g. 10 times) and then calculate the average. I don't have time to do that so I have only taken one measurement. For this purpose, it is safe to say that for every 1 woodcutter added the variation of total trunks collected will increase by ±2. For example the total trunks collected by 8 woodcutters can vary between repetitions by 16 trunks in the worst case - normally it will be less.
Results:
1. Pair Style is the best way to put woodcutters. It saves space and has absolutely no effect on tree production efficiency up to 5 woodcutters.
2. I was very surprised to see that up to 5 woodcutters can work in Pair Style with only 1 spacing and still have optimum tree production provided they have free plantation area with nothing blocking it. There is negligible improvement by increasing the distance between 5 woodcutters. For 6 woodcutters, optimum spacing is 2 and very little improvement can be gained by increasing the spacing more than 2. For 7 woodcutters the optimum spacing is 3. For 8 woodcutters the optimum spacing is 5.
Hope this helps

. I will test more configurations in the near future and post more results here. My next step is to check the optimum spacing when free plantation area is not available.
Here is the data. The number of tree trunks produced in 120 minutes:
